Unknown mark 'JTS' and 'hammer' symbol on 'plated?' milk jug

I am trying to determine the age and who the maker of this milk jug (which is part of a complete tea service) was. The letters JTS with a hammer symbol and numbers 878 are stamped on what I am assuming is plate ware. I have trawled through this and many other silver web sites to no avail. The complete set was bought from an antique shop in the late 1960’s.

Any information however small would be much appreciated.

Regards

Bill Davies